This invention relates to probes for use in imaging and, in particular, to probes for use in in vivo imaging of microscopic internal regions of a patient's body using magnetic resonance techniques.
In some conventional systems for in vivo imaging of internal tissues, a probe is inserted into a channel, normally a naturally-occurring channel, in the body to collect signals representative of the tissue surface to be imaged, and pass the signals to image processing means.
Where the regions to be imaged are microscopically small e.g. of diameter of no more than 1.5 mm, it is difficult to achieve satisfactory resolution.
When using magnetic resonance imaging techniques, the problem arises that water molecules have a diffusion coefficient of around 3.5.times.10.sup.-3 mm.sup.2 /s at 37.degree. C. in bulk water and the diffusion coefficient of water molecules in body tissue is likely to be much the same. In imaging systems, the time interval between RF excitation of a region and magnetic resonance data acquisition is of the order of 10 ms. Hence, half of the molecules originally excited in one part of the body tissue will have diffused over a distance of around 8 microns before their signals are acquired. Reducing the time interval between excitation and data acquisition requires wider acquisition bandwidths to be used, thus decreasing the signal to noise ratio, and also makes it necessary for stronger spatially encoding gradients to be used. Localised cooling of tissue may slow down diffusion, but this produces only a minor reduction in diffusion before the water molecules begin to form ice.
It is an object of the present invention to provide probes for use in in vivo imaging of a microscopic internal region of a body in which the above mentioned problems are alleviated.